Process for producing steel by electro-forming and carburization



United States Patent PROCESS FOR PRODUCING STEEL BY ELECTRO- FORMING AND CARBURIZATION John F. Lakner, Los Alamos, N. Mex., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application June 29, 1953, Serial No. 364,951

4 Claims. (Cl. 148-19) This invention relates to a process for producing steel by electroforming and carburization and more particularly to a process for producing carbon steel articles of manufacture by electroforming with iron upon a refractory carbide mandrel and carburizing the iron while still in place on the mandrel.

In manufacturing metal products, especially those of reduced wall thickness and irregular shape, no process or manufacturing technique has been developed for producing such products of steel except by arduous and expensive machining and turning operations. The machining or turning of inside diameters, especially, makes the machining methods expensive and impractical if close tolerances are necessary. Complex forms present more difiicult, if not impossible, machining problems.

The manufacture of thin walled articles has been most satisfactorily accomplished by electroforming, which is the production, or reproduction, of such articles by the electrodeposition of metals. One objection to this manufacturing process, however, is the inability to produce an article of any material except those metals which may be deposited by electrolysis; such metals include copper, sliver, gold, nickel, zinc, cadmium, chromium and iron. The limitations, therefore, in a choice of metals which may be used to manufacture an article by electroforming has been a serious one.

For example, if an article is needed which has the form of a seamless thin walled cylinder surmounted at one end by a frusto-conical section in which the wall thickness varies, and which is desired to be made of steel for certain physical properties, a choice of two methods of manufacture has heretofore been possible. The article may be machined by time consuming and complicated machining techniques which are made even more diflicult if close tolerances are required; or it may be manufactured by electroforming, in which case a substitute metal must be used at a sacrifice of some of the physical properties which are desired and present in steel. The second method is usually chosen, with nickel often used as a substitute for steel.

An object of the present invention is to provide a process for forming carbon steel articles by the electrodeposition of iron and carburization.

Another object of the present invention is to provide a process whereby electrodeposited iron may be carburized while on the plating mandrel without fusing thereto.

A further object of the present invention is to provide a process whereby thin walled articles of electrolytic iron may be subjected to the amount of heat necessary in carburizing without warpage or distortion.

It is a further object of the present invention to provide a class of refractory mandrels to be used as the cathode in the electrolytic plating of iron which will not fuse with the iron when subjected to the high temperatures necessary for carburization.

The present invention comprises the process of electroforming with iron upon a refractory carbide mandrel,

2,758,950 Patented Aug. 14, 1956 ice treating of the electroformed iron article by carburization while the electroformed article remains on the mandrel, tempering of the electroformed article, machining to outside finished dirnensions and removing the plate or article from the mandrel.

Although it has long been known that iron can be deposited from its solutions by electrolysis, the process has been little used except in the electrorefining of pure iron for special purposes and the building up of worn or undersized parts. The cheapness and availability of iron has been overshadowed by its poor physical properties in the state of a pure metal. Various methods of treating a deposited iron form to obtain steel have been tried but have proved unsuccessful prior to this invention. In the state of the art prior to the present invention, heat treating of the formed article after removal from the mandrel resulted in warpage and distortion of the article. Heat treating or carburization of the formed article while still in place on the mandrel, however, caused the iron to fuse with the mandrel due to the high temperature required, to such an extent that it could not be removed undamaged.

The present invention bridges the gap between electroforming with a substitute metal and expensive and impractical machining techniques, by providing a process whereby complex articles can be made by a method of electroforming and treating to produce an electroformed article of carbon steel. The principles and techniques of plating and electroforming with iron are well known to the art, however, some values and compositions for the plating bath and other variable factors are given hereinafter for a typical application to allow an accurate comparison between electroformed iron and the electroformed steel produced in accordance with the teachings of the present invention.

Ferrous sulfate or ferrous chloride solutions may be used as the plating bath in the electroforming of iron, however, for purposes of the present description a ferrous chloride bath was chosen. Although either solution is satisfactory, ferrous chloride is usually preferable since it produces ductile deposits in thick plates.

For purposes of comparison, the physical properties are given below for electroformed iron deposited from a typical iron plating bath which analyzed as 37.6 ounces of ferrous chloride and 43.1 ounces of calcium chloride per gallon of water. The bath was operated at a temperature of 194 F., with a current density of 50 amperes per square foot, and a pH of 0.5 The resulting electroformed iron has a tensile strength of 70,700 pounds per square inch, a 0.2% yield of 57,300 p. s. i., 8% elongation in /2 inch, 6% elongation in 1 inch, 5% elongation in 2 inches, a modulus of elasticity of 28.4 10 and a diamond point hardness value of 183.

In the process disclosed by the present invention, the iron is deposited on a refractory carbide mandrel selected from a class comprising titanium carbide, tungsten carbide, zirconium carbide, boron carbide, silicon carbide and chromium carbide. The refractory carbide mandrel is pressed to the desired form either with or without a binder. The presently preferred embodiment is a solid titanium carbide mandrel containing 10% chromium as a bonding agent pressed to the required shape.

The iron is electroformed upon the refractory carbide mandrel to the desired thickness in a ferrous chloride plating bath under operating conditions as described hereinbefore. The iron form on the refractory carbide mandrel is then carburized at temperatures and for periods of time well known to the art. The most satisfactory carburizing temperature to be used in the process of the present invention is found to be approximately 1650 F. The iron may be carburized to any predetermined depth or to its full thickness,

After carburizing, the electroformed article is tempered by quenching in oil and drawing to a desired hardness.

The final step of the process disclosed in the present invention comprises turning or finishing ofthe outside surface of the formed article to the desired final dimensions and removal from the mandrel.

The following physical properties of electroformed steel produced by the process of the present invention are given for comparison with the properties of electroformed iron stated hereinbefore.

Byelectroforming iron on a titanium carbide mandrel from a ferrous chloride'bath under plating conditions similar to those previously stated, carburizing the electroformed article while in place on the mandrel at a temperature of 1650 F. for 12 hours to a depth of 0.020 inch, Quenching in oil, and drawing to a temperature of 900 F. thefo'llowing properties were obtained; tensile strength 139,000 pounds per square inch; yield point 101,700 p. s. i.; elongation, 12 /z% in /2 inch, 8 2% in 9 in 7% i in es mo u f e s ici 30.3 t 105; diamond point hardness 28.0.

he @W 9 t process of h P e i nt o is he u e f fra o ma eria as t e elcctroforming m ndr M ta ic a dre of the pr r rt c n be used if the iron is to be hardened by carburizing while remaining on the mandrel due to the fact that some solution .of-the iron occurs in the metallic mandrel surface at the carbnrizing temperature. By using titanium carhide, or one of the aforementioned group of refractory carbides as the material of the clectroforrning mandrel, fusion'of-the iron with the mandrel will not result since these materials resist oxidation and fusion up to a mininrum temperature of 1850 F. Since the mandrel is conductive the electroforming process is simplified, and the mandrel may be repeatedly used.

In addition to the solid refractory carbide mandrels a metallic mandrel having its surface covered by one of the carbides of the aforementioned group may be used. With a mandrel of this type, the refractory carbide acts as a separating media between the metallic portion of the mandrel and the plated iron. An example of such a mandrel is a steel mandrel having a tungsten carbide plate of .001 to .003 inch bonded to its surface.

As an alternative to a refractory carbide mandrel of the class described hereinbefore a ceramic mandrel of lithium aluminum silicate may also be used. Since this material is non-conductive, it is necessary that a conductive coating be applied. 1

It is obvious that the process described herein may be varied by the use of two mandrels. In such a-process the iron is plated on'any mandrel of the prior art, machined and the shell removed. Then the shell is placed on a non fusing mandrel of the class described herein which is identical in'shape and dimension to the original plating mandrel. Upon the second non-fusing mandrel the 'electrofornied shell is then carburized and heat treated.

It will thus be'seenrthat whathas been described herein is a process by which carbon steel articles of manufacture, especially those having reduced wall thickness; may he produced by electroforming with iron and treating to result in an end product of carbon. steel,

hat i Fl m d i p e f r' r dn in rb n 1 4 Y manufacture comprising forming a body of a refractory carbide material selected "from the group consisting of titanium carbide, tungsten carbide, zirconium carbide, boron carbide, silicon carbide and chromium carbide, said body having an outside surface conforming with the inside configuration of said article to be produced; electroforming with iron upon said refractory carbide body to form an iron shell; carburizing said formed iron shell While in place on said refractory carbide body; heat treating said earburized shell; and removing said can.

burized heat treated shell from said refractory carbide body.

2. A process for producing carbon steel thin wall shells comprising forming a bonded refractory carbide body having an outside surface conforming with the inside configuration of said shell to be produced, said body being formed of a bonded refractory carbide material selected from the group consisting of titanium carbide, tungsten carbide, Zirconium carbide, boron carbide,- silicon carbide and chromium carbide; electroforming with iron uponsaid refractory carbide body to form a pure iron shell; carburizing said formed article while in place on said refractory carbide body at a temperature of approximately 1650 F.; quenching said article .in oil and drawing to hardness; finishing the outside surface of said articleand removing said article from said refractory carbide body.

3. A process for producing carbon steel articles of manufacture comprising forming a body having an outer surface conforming with the inside configuration of the article to be produced, said body having a sur ace of refractory carbide material selected from the group con? sisting of titanium carbide, tungsten carbide, zirconium carbide, .boron carbide, silicon carbide and, chromium can; hide; ielectroforming with iron upon said body to form an iron shell; carburizing said iron shell While in place on said body at a temperature of approximately 1650 'R; quenching said iron shell in oil and drawing to hardness; the outside surface of said shell and removing said shell from said body.

4. A process for producing a carbon steel article of manufacture comprising forming a body of titanium carbide bonded with 10 per cent chromium, said body having an outside surface conforming with the inside configuration of said article to be produced, electroforming with iron upon said titanium carbide body to form an iron shell, carburizing said formed iron shell while in place on said titanium carbide body, heat treat ing-said carburized shell, and removing said carburized heat treated shell from said titanium carbide body.

References Cited in the file of this patent TE ST E ATE TS 

1. A PROCESS FOR PRODUCING A CARBON STEEL ARTICLE OF MANUFACTURE COMPRISING FORMING A BODY OF A REFRACTORY CARBIDE MATERIAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM CARBIDE, TUNGSTEN CARBIDE, ZIRCONIUM CARBIDE, BORON CARBIDE, SILICON CARBIDE AND CHROMIUM CARBIDE, SAID BODY HAVING AN OUTSIDE SURFACE CONFORMING WITH THE INSIDE CONFIGURATION OF SAID ARTICLE TO BE PRODUCED; ELECTROFORMING WITH IRON UPON SAID REFRACTORY CARBIDE BODY TO FORM AN IRON SHELL; CARBURIZING SAID FORMED IRON SHELL WHILE IN PLACE ON SAID REFRACTORY CARBIDE BODY; HEAT TREATING SAID CARBURIZED SHELL; AND REMOVING SAID CARBURIZED HEAT TREATED SHELL FROM SAID REFRACTORY CARBIDE BODY. 